Allow limiting sparse run

Today, we always pass C=2 to enable sparse run on all the files.
Instead, allow C=1 to also be used to obtain sparse report on only the
files being recompiled.

Author: rnav

README.md

@@ -95,14 +95,16 @@ Other options
 
 As mentioned above you pass the make -j factor with `JFACTOR=n`.
 
-To run sparse use the `ubuntu@21.10` image and pass `SPARSE=1`.
+To run sparse use the `ubuntu@21.10` image and pass `SPARSE=2`.
 
 ```
-$ make SRC=~/src/linux kernel@ppc64le@ubuntu@21.10 SPARSE=1 JFACTOR=$(nproc)
+$ make SRC=~/src/linux kernel@ppc64le@ubuntu@21.10 SPARSE=2 JFACTOR=$(nproc)
 ```
 
 The log will be in eg. `output/ppc64le@ubuntu@21.10/ppc64le_defconfig/sparse.log`.
 
+To only run sparse on files being recompiled, pass `SPARSE=1`.
+
 To build modules pass `MODULES=1`
 
 To convert all modules to builtin, pass `MOD2YES=1`.

build/scripts/container-build.sh

@@ -86,7 +86,7 @@ if [[ "$1" == "kernel" ]]; then
         if [[ -n "$SPARSE" ]]; then
             rm -f /output/sparse.log
             touch /output/sparse.log
-            (set -x; make C=2 CF=">> /output/sparse.log 2>&1" $verbose $quiet "$cc" -j $JFACTOR)
+            (set -x; make C=$SPARSE CF=">> /output/sparse.log 2>&1" $verbose $quiet "$cc" -j $JFACTOR)
 
             rc=$?